1. Field of the Invention
The present invention relates to a large strain-introducing working method and a caliber rolling device for use in the working method.
2. Description of the Related Art
As a steel bar manufacturing method, there has been generally known a caliber rolling method using rolls having caliber grooves. Caliber shapes can be generally categorized as either angular (e.g., square or diamond), oval, or round. By combining these calibers properly (in a “pass schedule”), the cross-sectional area of a work piece can be efficiently reduced, and the work piece can be finished into a wire rod of a predetermined size. At this time, it is important to find a way to reduce the cross-sectional area efficiently and, thereby, achieve a predetermined shape precisely.
In the caliber designs of the prior art, however, attention has only focused on the area reduction ratio and the cross-section shape. This is problematic because the metal structure is coarser at the center than on the surfaces. This is mainly caused by the fact that a strain equivalent to that on the surface is not introduced into the central portion of the metal structure. If, therefore, a large strain can be introduced into the entire metal structure with an area reduction ratio and a pass number similar to or smaller than those of the prior art, the structural homogeneity can be enhanced to industrially generate a metal structure having a fine grain structure.
Also, the above-mentioned caliber designs are intended for hot working. In hot working, the strain or stress introduced in one pass can be released by the recovery/recrystallization of the structure between the passes. This raises a problem that the influences of the strain distribution introduced after one pass upon the strain distribution and the cross-sectional shape after the following pass cannot be estimated.
Therefore, an objective of the present invention is to solve the aforementioned problems of the prior art and to provide a novel technical means for clarifying the influences of the strain distribution introduced in the first pass upon the strain distribution and the cross-section shape after the next pass, thus enabling introduction of large strain into the entire cross-section of a material, particularly at the center of the material.